1. Field of the Invention
The present invention relates to a communications receiver for receiving messages, such as a radiopager. In the present specification the term radiopager refers to a communications receiver for receiving only an address codeword or an address codeword together with concatenated data message codewords. Normally such receivers are not able to transmit signals, although what is termed answer-back radiopagers are becoming available. For convenience of description, the invention will be described in terms of its use in a POCSAG or CCIR Radiopaging Code No. 1 system the details of which system are described in "The Book of the CCIR Radiopaging Code No. 1," available from Secretary RCSG, British Telecom, Radiopaging, 23 Howland Street, London, W1P 6HQ, United Kingdom. However the teachings of the invention are not system dependent and could readily be applied to radiopagers operating in accordance with the Golay or ERMES radiopaging protocols.
2. Description of the Related Art
In the United Kingdom, POCSAG digital radiopaging services are provided by several network providers. However the service providers also supply radiopaging receivers to the end user and bill the customer at periodic intervals, such as every 3 months. When supplying a radiopager, a service provider writes a radio identity code (RIC) or address in a non-volatile store included therein. The RIC uniquely links that radiopager with the particular user. Thus, in operation, if the radiopager detects its RIC in the relevant predetermined frame of a transmitted batch, it remains energised to provide an audio, visual and/or tactile alert indication to the user, and when appropriate will store message data which is concatenated with the RIC address codeword. The service provider will also adjust the receiver to receive signals in the relevant frequency channel, the bit rate being already predetermined by the POCSAG protocol. The radiopager as delivered to the end customer is then able to operate within the receiving range of transmitters operated by a predetermined network provider.
At the present time many countries have their own national digital paging systems based on POCSAG. However, because of the likelihood of the same RIC being issued to a different pager in each country, and each country operating its paging system on a different frequency or frequencies, it is not usually possible for a user to take a normal UK digital radiopager to another country which is also on the POCSAG system and use it there. Furthermore, no arrangements currently exist for billing users who cross national boundaries.
A number of PTTs and other network providers in Europe operate Euromessage, which is an attempt to provide a degree of international paging coverage within certain parts of Europe, primarily the major cities. Euromessage operates on a single frequency at UHF, and requires a user to hire a radiopaging receiver from a service provider. It also requires the user to indicate, several weeks in advance of his departure, those countries in which the user wishes to be paged. Drawbacks to Euromessage are that it is relatively inflexible, is not comprehensive in its coverage of the respective countries, and requires a user to have to carry a second radiopaging receiver in addition to that usable in his home country.